java—在尝试自动连线时获取spring托管类上的nullpointer

e4yzc0pl 于 2021-07-23 发布在 Java

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我正在创建一个spring-boot应用程序来侦听rabbit队列并将消息转发到kafka流。我正在努力 @Autowire Kafka配置类，但我得到 NullPointerException ，更令人惊讶的是，当我列出所有spring管理的bean时，它会给出我正在尝试的类的对象名 @Autowire . 我不知道我在哪里失踪了。
起始类：

@SpringBootApplication
@ComponentScan(basePackages = {"com.example.demo.service","com.example.demo.configuration"})
public class RabbitConsumerApplication {

    private static ApplicationContext applicationContext;

    public static void main(String[] args) {
        applicationContext = SpringApplication.run(RabbitConsumerApplication.class, args);
        displayAllBeans();
    }

    public static void displayAllBeans() {
        String[] allBeanNames = applicationContext.getBeanDefinitionNames();
        for(String beanName : allBeanNames) {
            System.out.println(beanName);
        }
    }

}

kafkaproducerservice类：

package com.example.demo.service;

@Component
public class KafkaProducerService {

    @Autowired
    private KafkaTemplate<?, String> kafkaTemplate;

    public void getMessageFromMQ(Message  message) throws InterruptedException {

        Map<String, Object> configProps = new HashMap<>();
          configProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
          configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
          configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
          DefaultKafkaProducerFactory<Object, Object> defaultKafkaProducerFactory = new DefaultKafkaProducerFactory<>(configProps);

        kafkaTemplate.send("testTopic",new String(message.getBody()));

    }

    @Override
    public String toString() {
        return "KafkaProducerService [kafkaTemplate=" + kafkaTemplate + "]";
    }

}

kafkaproducerconfig类：

package com.example.demo.configuration;

@Configuration
public class KafkaProducerConfig {

    @Bean
    public ProducerFactory<String, String> producerFactory() {
      Map<String, Object> configProps = new HashMap<>();
      configProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
      configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
      configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
      return new DefaultKafkaProducerFactory<>(configProps);
    }

    @Bean
    public KafkaTemplate<String, String> kafkaTemplate() {
      return new KafkaTemplate<>(producerFactory());
    }
}

rabbitlistenerservice类：

package com.example.demo.service;

public class RabbitListenerService implements MessageListener{

    @Autowired
    private KafkaProducerService kafkaProducerService;

    @Override
    public void onMessage(Message message) {
        System.out.println("message :"+new String(message.getBody()));
        System.out.println("object:"+kafkaProducerService.toString());  //19th line. getting nullpointer on this line   
    }

}

堆栈跟踪：

2021-02-20 13:55:06.750  WARN 5392 --- [tnerContainer-1] s.a.r.l.ConditionalRejectingErrorHandler : Execution of Rabbit message listener failed.

org.springframework.amqp.rabbit.support.ListenerExecutionFailedException: Listener threw exception
    at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.wrapToListenerExecutionFailedExceptionIfNeeded(AbstractMessageListenerContainer.java:1746) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.doInvokeListener(AbstractMessageListenerContainer.java:1692) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.actualInvokeListener(AbstractMessageListenerContainer.java:1562) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.invokeListener(AbstractMessageListenerContainer.java:1539) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.doExecuteListener(AbstractMessageListenerContainer.java:1530) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.executeListener(AbstractMessageListenerContainer.java:1474) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.doReceiveAndExecute(SimpleMessageListenerContainer.java:967) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.receiveAndExecute(SimpleMessageListenerContainer.java:913) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.access$1600(SimpleMessageListenerContainer.java:83) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer$AsyncMessageProcessingConsumer.mainLoop(SimpleMessageListenerContainer.java:1288) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer$AsyncMessageProcessingConsumer.run(SimpleMessageListenerContainer.java:1194) ~[spring-rabbit-2.3.4.jar:2.3.4]
    at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]
Caused by: java.lang.NullPointerException: null
    at com.example.demo.service.RabbitListenerService.onMessage(RabbitListenerService.java:19) ~[classes/:na]
    at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.doInvokeListener(AbstractMessageListenerContainer.java:1688) ~[spring-rabbit-2.3.4.jar:2.3.4]
    ... 10 common frames omitted

message :hey you
message :hey you

我只是想 @Autowire kafkaproducerservice类进入rabbitlistenerservice。

Java spring spring-boot Autowired

来源：https://stackoverflow.com/questions/66289553/getting-nullpointer-on-a-spring-managed-class-when-trying-to-autowire

3条答案

按热度按时间

sqserrrh1#

好吧，我解决了这个问题。即使@autowire发生了，但它实际上绑定了一个空对象，因为在rabbitconfig.java中，我实际上用一个新关键字初始化了rabbitlistenerservice，而spring ioc不处理它。我改变了方式，解决了问题。
rabbitlistenerservice.java文件

@Component
public class RabbitListenerService implements MessageListener{

    @Autowired
    private KafkaProducerService kafkaProducerService;

    @Override
    public void onMessage(Message message) {
        System.out.println("message :"+new String(message.getBody()));
        System.out.println("object:"+kafkaProducerService.toString());

        try {
            kafkaProducerService.getMessageFromMQ(message);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

然后将rabbitlistenerservice自动连接到rabbitconfig
rabbitconfig.java文件

@Configuration
public class RabbitConfig {

    private static final String my_queue = "TestQueue";

    @Autowired
    private RabbitListenerService rabbitListenerService;

    @Bean
    MessageListenerContainer messageListnerContainer() {

        SimpleMessageListenerContainer simpleMessageListenerContainer = new SimpleMessageListenerContainer();
        simpleMessageListenerContainer.setConnectionFactory(connectionFactory());
        simpleMessageListenerContainer.setQueues(myQueue());
        simpleMessageListenerContainer.setMessageListener(rabbitListenerService);
        return simpleMessageListenerContainer;

    }

}

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f8rj6qna2#

从您的代码来看，您似乎还没有定义任何kafka模板bean。例如：

@Configuration
public class MyKafkaConfig {

    ...

    @Bean
    public KafkaTemplate<String, String> kafkaTemplate() {
        // define a template here
    }
}

定义的kafka服务具有注入（自动连线） KafkaTemplate<?, String> . 这样的bean是在配置类中定义的吗？
也请张贴您的stacktrace。

赞(0）回复(0）举报 2021-07-23

6gpjuf903#

试试这个，把包换成 * ，确保它在bean列表中打印kafkaproducerservice，
经常练习为impl服务类创建接口

@Component
public class KafkaProducerServiceImpl implements KafkaProducerService

例如

@SpringBootApplication
    @ComponentScan(basePackages = "com.example.demo.*"})
    public class RabbitConsumerApplication {

  ...
    }

赞(0）回复(0）举报 2021-07-23

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java—在尝试自动连线时获取spring托管类上的nullpointer

3条答案

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